For several years hybrid solid state system such as infrared detectors have been successfully incorporated into integrated circuits for mass production and miniaturization. Typically, such infrared detectors are fabricated in N.times.M arrays of infrared detector elements or thermal sensors. Each element in the array may itself be fabricated from semiconductor materials such as alloys of mercury, cadmium, and tellurium ("HgCdTe") which are operable to generate electron-hole pairs when struck by infrared radiation. The particular wavelength from which each element generates electron-hole pairs may be tuned by adjusting the ratio of mercury to cadmium in the semiconductor material. Infrared detectors typically sense electromagnetic radiation having a wavelength, generally, between 0.5 and 15 .mu.m corresponding to an energy level of 2 to 0.1 eV.
Common applications for thermal sensors include thermal (infrared) imaging devices such as night vision equipment or target acquisition and tracking systems. One such class of thermal imaging devices includes a focal plane array of infrared detector elements or thermal sensors coupled to an integrated circuit substrate or silicon processor with a plurality of vias extending between the focal plane array and the integrated circuit substrate. The thermal sensors define the respective picture elements (or pixels) of the resulting thermal image. Examples of such infrared detectors and associated vias or metal interconnects between thermal sensors in a focal plane array and a silicon processor are shown in U.S. Pat. No. 4,447,291 entitled Methods for Via Formation in HgCdTe, and U.S. Pat. No. 5,144,138 entitled Infrared Detector and Method. For some infrared detectors the metal interconnect pattern is formed by using metal lift off techniques with evaporated indium or indium/lead/indium metal films.